- Details
- Category: Конкурсы Российского научного фонда (РНФ)
- Published: 08 December 2022
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Russian Science Foundation Project No. 22-21-00572 " Development of laboratory model of general atmospheric circulation ".
Project leader:
Sukhanovskii Andrei , senior researcher, D.Sc. ICMM UB RAS (Perm, Russia).
Project objectives:
The project aims to create and validate a laboratory model of the general circulation of the atmosphere.
At present, the most widely used model of general atmospheric circulation is a gap between two coaxial cylinders, on the walls of which different temperature values are set. This approach quite effectively models the large-scale circulation in the middle latitudes. However, the general atmospheric circulation has a more complex structure and consists of several cells (Hadley, Ferrell, and polar), the seasonal intensity of which can vary appreciably. It leads to the problem of the atmospheric circulation modeling in a more realistic framework. The project participants, varying the layer thickness, the distance between heating and cooling sources, their intensity, and the bottom slope, plan to realize the meridional circulation in the form of three cells. The implemented laboratory model will serve as the basis for solving a whole set of problems linked to the baroclinic waves in atmosphere.
Supplementary materials:
video (in a rotating frame, accelerated 10 times)
Summary final report on the results of the second year of the RNF project No. 22-21-00572:
A new model of the general circulation of the atmosphere has been developed, which represents a rotating liquid layer with an aspect ratio noticeably less than unity, with a localized rim heater located at the periphery of the bottom and a disk-shaped cooler placed in the central part, at the upper boundary of the liquid layer. The rim heater simulates heating in the equatorial region and the cooler, cooling in the polar region. The heater is specially displaced from the side wall to minimize its influence on the formation of flows, due to non-slip condition at the boundary.
Based on the developed principal scheme, an experimental model was realized, which is a tank of square cross-section with a side of 700 mm and a height of 200 mm. To realize the cylindrical layer, an additional cylindrical wall made of Plexiglas with a thickness of 3 mm and radius R = 345 mm was inserted into the tank. At the bottom there is a rim, electric heater with a width of 25 mm. The distance from the side wall to the outer boundary of the heater is 40 mm. Cooling of the liquid is provided by heat exchange with ambient air on the free surface (room temperature is kept constant by the air conditioning system), a cooler located in the central part of the upper boundary, and heat flow through the side wall. Aluminum powder was used to visualize the flow pattern in the upper layer. Images were captured using a Bobcat 2020 4 megapixel CCD camera.
Experimental measurements provide only partial information about the system under study, therefore, to reconstruct the three-dimensional structure of the flow, a direct numerical simulation of thermal convection in a rotating cylindrical layer was performed using the freely distributable computational fluid dynamics package OpenFOAM v2106. The computational domain is a digital copy of the experimental model in terms of its geometric dimensions, location of the heater and cooler.
The solution of the main task of the project required a large number of experiments and numerical simulations. Heating power (from 8 to 120 W), rotation speed (from 0.08 to 0.48 rad/s), layer thickness (3 cm and 6 cm), physical properties of the liquid (water and PMS-5, Prandtl numbers 5.4 and 63) were varied. A large amount of data obtained by experiments and mathematical modeling was analyzed. On the basis of these results three papers were prepared and published, including in two high-level journals specializing in geophysical topics (Q2), one more paper has been prepared and is under review.
The following can be highlighted as the main results obtained in the frame of the project:
- the principal differences in the formation of mean large-scale flows and baroclinic waves in different atmospheric circulation models are shown. An important difference of the presented model from classical annulus configurations is the absence of steady waves. All wave modes, even with a regular wave structure, are characterized by strong non-periodic fluctuations. The observed baroclinic wave structures are a combination of different baroclinic modes evolving in time. This proves that the spatial distribution of heating and cooling, their location, and the type of boundary condition are important for the stability of baroclinic waves. With increasing rotational velocity, the waves in our model become irregular and represent a set of azimuthal wave modes, the main energy of which is contained in modes from m=2 to m=8, which agrees well with the data for the real atmosphere. A map of regimes in the plane of the thermal Rossby number-Taylor number is constructed.
- the influence of processes in the Ekman layer on the formation of mean flows and baroclinic waves was analyzed. The analysis was carried out on the basis of data from numerical calculations. It is shown that the main source of meridional circulation is thermal convection, and the radial flows induced in the viscous boundary layer are not of primary importance. The distribution of velocity fluctuations shows that, except for the heating region, they are mainly concentrated in the upper layer. The velocity fluctuations are damped in the Ekman layer, and as a result the baroclinic waves in our model are localized in the upper layer. It is consistent with the results of other authors, both for the laboratory system and for the real atmosphere.
- the most important result of the project is the successful realization in the laboratory model of the flows whose structure is qualitatively similar to the circulation in the real atmosphere. The model allows us to obtain the meridional circulation consisting of three cells, analogs of Hadley, Ferrel (of baroclinic wave nature) and polar cells. The structure of baroclinic waves, the location of their formation, and the mode composition are also similar to what is observed in the atmosphere. It is shown that the atmospheric mode in the laboratory model is realized only in a limited range of parameters. Decreasing the rotation rate leads to regularization of baroclinic waves, and increasing the rotation rate on the contrary leads to destruction of long waves and geostrophic turbulence. The realized model makes it possible to carry out long-term controlled experiments and can serve as an effective tool for studying various aspects of the global atmospheric circulation.
- to study the influence of the beta effect on the structure of mean flows and baroclinic waves, experiments and numerical simulations with a sloping bottom were realized. The simulations showed that a twofold change in the aspect ratio (from 0.09 to 0.17) does not lead to a qualitative change in the structure of the mean meridional circulation. A relatively small tilt (5 degrees) leads to noticeable quantitative changes in the fluid flow, preserving the overall flow structure. However, a further increase of the inclination up to 10 degrees leads to crucial changes both in the flow structure and in the intensity of wave motions. The formation of a downward cold flow due to the bottom slope (analog of slope currents) has a strong influence on the current structure. The presence of bottom slope leads to intensification of wave motions. Transformation of the meridional circulation at large tilts leads to noticeable changes of zonal flows, in particular, to the formation of an anticyclonic circulation near the bottom. The general changes in the structure and dynamics of flows lead to noticeable changes in the mean temperature distribution. Experiments were carried out for an inclination angle of 5 degrees, a fixed heating power (120 W), two layer thicknesses (35 mm and 60 mm), three rotational velocities of 0.11 rad/s (mode without baroclinic waves), 0.23 rad/s (mode of regular unsteady baroclinic waves), and 0.37 rad/s. Qualitative analysis of the observed flows showed that the beta effect has a significant influence on the structure and dynamics of the waves.
